1. Field of the Invention
The present invention relates to a scanning optical system most suitable for a writing optical system in a laser printer, a digital copying machine, a facsimile, etc. in which a scanned face is scanned by a light beam from a semiconductor laser or a light-emitting diode as a light source, and an optical system in a reading device, a laser display, a laser measuring device, etc.
2. Description of the Related Art
In a recorder such as a laser printer, a scanning optical system is used to write information to a suitable recording medium.
In the scanning optical system, when an f.theta. lens constituting a lens for optical scanning is made of plastic, the changes in shape, refractive index, etc. of this lens are caused by the change in environment, especially, the change in temperature. Therefore, the position of a formed image point in the vicinity of the scanned face is changed so that it is difficult to stably provide the uniform diameter of a beam spot on the scanned face.
In lens correction methods shown in Japanese Patent Application Laying Open (KOKAI) Nos. 63-7530 and 61-150394, the problems about the change in focal length of the f.theta. lens caused by the change in environmental temperature are still not solved. Therefore, it is desirable to provide an optical scanning system for generally solving the above-mentioned problems.